The invention described herein was made in the performance of work under a NASA contract, and is subject to the provisions of Public Law 96-517 (35 U.S.C. xc2xa7202) in which the Contractor has elected to retain title.
This invention relates to vibratory gyroscopes, and more particularly to silicon micromachined vibratory gyroscopes.
Multi-axis sensors are highly desirable for inertial sensing of motion in three dimensions. Previously, such sensors were constructed of relatively large and expensive electromagnetic and optical devices. More recently, micromechanical sensors have been fabricated using semiconductor processing techniques. Microelectrical mechanical or xe2x80x9cMEMSxe2x80x9d systems allow formation of physical features using semiconductor materials and processing techniques. These techniques enable the physical features to have relatively small sizes and be precise. Specifically, micromechanical accelerometers and gyroscopes have been formed from silicon wafers by using photolithographic and etching techniques. Such microfabricated sensors hold the promise of large scale production and therefore low cost.
The integration of three gyroscopic sensors to measure the rotation rates about the three separate axes coupled with three accelerometric sensors to measure the acceleration along the three axes on a single chip would provide a monolithic, six degree-of-freedom inertial measurement system capable of measuring all possible translations and orientations of the chip. There has been some difficulty in constructing a high-performance, or sensitive vibratory rate gyroscope to measure the rotation about the axis normal to the plane of the silicon chip, i.e., the Z-axis.
In a vibratory gyroscope, the Coriolis effect induces energy transfer from the driver input vibratory mode to another mode which is sensed or output during rotation of the gyroscope. Silicon micromachined vibratory gyroscopes are integratable with silicon electronics. These devices are capable of achieving high Q factors, can withstand high g shocks due to their small masses, are insensitive to linear vibration and consume little power. However, most of these micromachined gyroscopes have a very small rotation response, since their input and output vibration modes have different mode shapes and resonant frequencies. The use of different resonant modes also makes these devices very temperature sensitive due to the different temperature dependency of each of the modes. These devices usually have very high resonant frequencies resulting in low responsitivity, since the Coriolis induced response is inversely proportional to the resonant frequency of the structure. Finally, due to the small mass of the structure, thermal noise limits the ultimate performance and use of microgyroscopes. For these reasons, micromachined vibratory gyroscopes have not been used for precision navigation and attitude control applications, but have been employed primarily for automotive applications in which extreme low cost is a major driving factor and performance is.set at a lower premium.
The present invention is a microgyroscope which uses the Coriolis force to detect the rotation rate. The microgyroscope may comprise a mechanical resonator. The microgyroscope comprises of a single vertical post which is the rotation rate sensing element. The vertical post is supported by four silicon suspension. The vertical post is driven electrostatically to oscillate in-plane (x and/or y directions) by vertical capacitors. The Coriolis force induced motions of the vertical post is detected capacitively by the vertical capacitors. A high performance and small gyroscope is desired for rotation detection of space craft, vehicles and platforms.